Film pre-winding for 35 mm format film cameras is a system with which a roll of unexposed 35 mm film can be fully wound up previously into the unexposed film chamber of the camera pulling the film out of the film cartridge before starting picture taking (giving exposures), and after each exposure the film is wound back into the film cartridge one frame by one frame, so that all the exposed frames are protected from being exposed twice by opening the camera back door accidentally.
In this type of film winding system, differently from the conventional type of film advancing, it is necessary to pull the unexposed film out of the film cartridge and to wind the unexposed film entirely over the take-up spool (or take-up drum) provided in the unexposed film chamber of the camera beforehand. Consequently the system to wind the unexposed film over the take-up spool must be added to the ordinary film winding mechanism. Inevitably the cost should be increased because of the additional mechanism and expensive electric parts for pre-winding control circuit. Due to this cost increase, today only some very expensive class 35 mm cameras use this pre-winding system for all this merit of pre-winding. In the world market today, such high end 35 mm compact cameras with the film pre-winding system like Fuji Super 145A, Super 120A, Super 90AZ compact 35 mm cameras which are all from Fuji Photo Film Co., Ltd. in Japan or such as Ricoh GR 1, GR 10, GR 21, R1 and R10 35 mm compact cameras, which are all from Ricoh Co., Ltd. in Japan are being sold. Other than the cameras mentioned above, there is practically none of the cameras with the film pre-winding system. Only a few cheap single use cameras have manual pre-winding mechanism, but to wind up a roll of unexposed film entirely over the take-up spool manually by hand it takes too much time and is not suitable for practical use. So all of the pre-winding system of the high end 35 mm cameras have motorized pre-winding system, and all of them control the film pre-winding and film winding back using a CPU (central processing unit-semiconductor).
However, such an electronically controlled pre-winding system is difficult to be provided in low cost. The manually controlled pre-winding mechanism by hand can be very low in cost, but users must pre-wind the film by handle or knob all the way to the end of film, which normally has maximum 36 exposures, and it cannot be suitable for practical use, unless the pre-winding is done by manufacturer using an automated pre-winding instrument in the factory before delivery just like the case of single use cameras.
If the film pre-winding can be done by motor, and if the film driving back and forth can be controlled mechanically using very inexpensive parts and a simple circuit instead of the expensive CPU controlled circuit and mechanism, such a film pre-winding mechanism can be fairly inexpensive in cost and quite suitable for practical use having the merit of the film pre-winding, namely protection of exposed film.
It is, therefore, an object of the present invention to provide a film pre-winding mechanism of 35 mm film format cameras using mechanical control of film pre-winding over the take-up spool and film winding back into the film cartridge without using any expensive electronic circuit with CPU.
To achieve the above object, the film pre-winding mechanism according to the present invention comprises a mechanical direction switch located on the camera body to change the motor rotation from pre-winding direction to winding back direction or in a reverse way, an actuator of the said mechanical direction switch which is coupled with the knob of the direction switch and controls the position of the knob of the direction switch, a spring which pulls the said actuator to keep the knob of the direction switch always at the pre-winding position, a means of actuator control provided on a part of the camera back door, and a film-sensing switch, which is located on a part of body where the film is running and which is turned on to rotate the motor by the pressure of the camera back door and the loaded film when the camera back door is closed with the film placed over it.
According to the present invention, when the camera back door is opened, the actuator is pulled by the spring immediately, and the knob of the direction switch is set at the pre-winding position, and the actuator and the knob of the direction switch are held at pre-winding position even after the camera back door is closed again. So, to load an unexposed film, the camera back door must be opened, and the instant that the camera back door is opened, the actuator and the knob of the direction switch are set at the film pre-winding position, and after the camera back door is closed with the loaded film again, the direction switch is still at the pre-winding position being ready to pre-wind the loaded film if the motor starts running.
The film driving circuit is so designed as to start pre-winding film automatically when the camera back door is closed with film loaded in the camera. When the loaded film and the closed camera back door together depress the film-sensing switch, it is turned on and the motor starts running immediately. And the unexposed film is to be pre-wound over the take-up spool in the unexposed film chamber automatically. After the unexposed film has been entirely pre-wound over the take-up spool or take-up drum in the unexposed film chamber, as the next step for picture taking, the knob of the direction switch should be moved manually by hand to the winding position, and then the motor rotation is switched to winding direction, and an unexposed frame of the film is pulled back out of the unexposed film chamber and placed at the picture taking position automatically, and the film driving stops there. And after depressing the shutter release button once, another unexposed frame of the film will be advanced to the picture taking position advancing the exposed frame into the film cartridge. When the last frame of the unexposed film is exposed, all the exposed frames of the film will have been wound back into the film cartridge and safely protected there.
In the case of conventional 35 mm cameras, the unexposed film should be kept in the film cartridge, and be advanced one frame by one frame after each exposure to the exposed film chamber of the camera, and after the roll of film has been fully exposed, the film must be re-wound back into the film cartridge. So all the exposed frames are stored in the exposed film chamber once, which is not light tight, and not stored in the safe light tight film cartridge. Therefore all the exposed frames will be completely damaged, if the camera back door is opened accidentally. With the present invention, the unexposed film is entirely pre-wound first into the unexposed film chamber, and then the unexposed film is pulled out of the unexposed film chamber one frame by one frame after each exposure, and all the exposed frames are wound back into the film cartridge which is perfectly light tight, so all the exposed frames are protected from the damage of accidental back door opening. The present invention is related to this pre-winding mechanism of the unexposed film.